# Tag Info

7

The first question as stated has a rather trivial answer: "If the sun magically disappeared, instantly, along with all its influences, how long would it take its gravity to stop having an effect on us?" Since the Sun's gravity is among its influences, it would instantly stop having an effect on us. That's just part of the magical situation, and doesn't ...

5

Dark matter, is just a name for something we know nothing of. It was named to account for an extra gravity source for which there have been indirect observations, but yet we cannot explain. The force of gravity exerted by light is negligibly small yet we have measured the gravitational pull of Dark Matter to be big enough to affect whole galaxies; it is ...

3

Here's an intuitive understanding without math or physics explanations (others will provide that stuff here): You are right that approaching and leaving the vicinity of a planet in itself adds up to zero effect. Gravity assist is the effect of being "dragged along" with the movement of the planet. If a spaceship approaches the planet from behind in its ...

2

The diagram is in the rest frame of the planet. Now suppose a spacecraft is slowing down in the frame of the solar system. A planet is nearby, so it now starts accelerating due to its gravity and gains speed. Now, this speed increase is added to some component of the speed of the planet's motion when it comes out on the other side (this added component can ...

2

Based on observable data, I assume that there is a relationship between the size, rigidity and the passage of time; that will result in all objects subject to only their own gravitational influences (Given: no body is ever truly uninfluenced by others) becoming spherically shaped (round). That's called hydrostatic equilibrium. That's one of the ...

2

As Yashbhatt said, we can detect light: with our eyes (visible light only) and with special machines. We can also see the effects of some type of lights. Dark matter, however, cannot be detected for now. Also, light is energy, dark matter is matter. Why does your skin tan? It's because of the ultraviolet light. Why are you hot each summer? It's because of ...

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Actually, "instant" gravity was part of Newton's theory of gravity. It is now understood that the "speed of gravity" is equal to the speed of light according to general relativity. http://en.wikipedia.org/wiki/Speed_of_gravity

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You could google "Maccone focal" for the most ardent proponent of this project (and I love it too, the most furthest meaningful mission possible within a life time, and what a view!) But others may have variations of his idea. One should be a bit wary about enthusiasts. Here's a link to some article where Maccone is cited to explain that planets need 6-17 ...

1

You are correct that an hyperbola's outgoing speed is the same as the incoming speed with regard to the body lieing at hyperbola's focus. The direction is changed. But with regard to another body, the change of direction can mean a change of speed. Here is a diagram of how the moon might be employed in the capture of an asteroid to reduce it's hyperbolic ...

1

No, there is no spherical volume of space within which objects all tend to approach us and thereby show blue-shift. The fact that the Andromeda galaxy is blue-shifted is because at these relatively small distances the cosmological red-shift is much smaller than further away. Andromeda's own (non-cosmological speed) is larger then the cosmological speed away ...

1

If you know the apoapsis and periapsis, you can find the eccentricity, using $r_a = a (1+e), r_p = a (1-e)$ (https://en.wikipedia.org/wiki/Apsis#Mathematical_formulae). Using the eccentricity, you can find the radius at any angle $\theta$ from the periapsis (this angle is also called the true anomaly). \$r(\theta) = \frac{a(1-e^2)}{1+e.\cos ...

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Light may account for a small portion of dark matter, but it is unlikely to account for most/all of it. From a Wikipedia article on dark matter: http://en.wikipedia.org/wiki/Dark_matter the total mass–energy of the known universe contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy.[2][3] Thus, dark matter is estimated to constitute ...

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